1. Field of the Invention
This invention relates to an electrochromic display (ECD) and an electrodeposition display (EDD), each comprising a plurality of isolated cells filled with an electrolytic fluid disposed between two electrodes.
2. Description of Related Art
Electrochemical displays, including electrochromic displays and electrodeposition displays, have been known for years and are attractive for portable display applications such as PDAs and e-books because they are reflective and may be driven at very low voltages. Electrochromic displays are non-light emission type display devices, the operation of which is based on reflection light or transmission light as a light control device through an electrochemical reaction and they broadly fall into three types: solution-based, intercalation (such as those disclosed in U.S. Pat. Nos. 6,172,794 and 6,245,262) and nanostructure. In the solution based electrochromic device, an organic electrochromic compound, such as one of viologens, is dissolved in an electrolyte solution and the solution is filled into an electrochemical cell comprising at least one transparent electrode. The electrochromic compound reversibly changes between the color and colorless states at the electrodes based on an electron transfer (reduction or oxidation) mechanism. Some of the drawbacks of this type of device are slow response rate due to the slow diffusion of redox active species towards the electrodes and low resolution and unacceptable stability of the electrochromic species for long-term operation. The second category of electrochromic devices is based on color change upon intercalation of small ions into a thin metal oxide film coated on conducting glass substrates. The performance of this type of device depends on the rate of ion transport into and out of the metal oxide film, which causes the switching time to be in the order of tens of seconds even for relatively small areas. Other disadvantages of this type of electrochromic devices include fading of color due to a certain degree of irreversibility of the diffused ion species to the metal oxide layer. The third category of the electrochromic displays uses nanostructure-film electrodes modified with electrochromophores. This type of electrochromic display represents an improvement over the other two types in terms of contrast ratio, switching rate and bi-stability (as reported in Fitzmaurice et. al. in U.S. Pat. No. 6,301,038; Cummings et.al., in J. Phys. Chem. B, 104, 11449 (2000); and U. Bach et. al. in Adv. Mater., 14, 845 (2002)). However, all three types of electrochromic devices can only be manufactured by a batch-wise process and moreover their resolution and color addressability remain unsatisfactory for many applications.
Electrodeposition displays (EDD) based on deposition/dissolution of metal salts particularly silver salts have been disclosed in SID 02 Digest, pp. 39-41 and U.S. Pat. Nos. 5,764,401, 5,864,420, 5,880,872 and 6,336,753, all issued to Sony Corporation. A typical EDD comprises two electrodes and a gel electrolyte consisting of a polymer matrix, a silver salt and a plasticizer or solvent. A reflective material such as TiO2 dispersion is typically used in the display cell to achieve high reflectance. By applying an appropriate voltage, the metal particles are deposited from the gel electrolyte onto a transparent electrode to show a colored state. Although the EDD described above addresses some of the drawbacks of the ECDs, such as the response time and contrast ratio, their usage is still limited due to certain problems. For example, no barrier or partition between pixels is present to confine the silver deposition within the addressed pixel. In addition, the silver metal tends to deposit all over the electrode which results in a poor image resolution. Although the image resolution may be improved by reducing the cell gap and optimizing the writing pulse width, color addressability of EDDs remains to be a major issue.
In view of the problems mentioned, improved ECDs and EDDs based on the microcup technology have been developed. Similar to the microcup based electrophoretic displays, the microcup based ECDs or EDDs of the present invention comprise a plurality of isolated cells (or microcups) filled with an electrolytic fluid disposed between two electrodes. The filled microcups may be sealed continuously with a sealing material by a one-pass or a two-pass process to achieve high resolution and color addressability. Other advantages of the microcup based ECDs and EDDs include superior physicomechanical properties such as impact and flexure resistance, compatibility with roll-to-roll manufacturing processes, format flexibility and low cost.
The microcup technology and related inventions are disclosed in co-pending applications, among them, Ser. No. 09/518,488, filed Mar. 3, 2000 (corresponding to WO01/67170), Ser. No. 10/087,527, filed Feb. 28, 2002, corresponding to US Publication No. 2002-0131152, Ser. No. 09/942,532, filed Aug. 29, 2001, corresponding to US Publication no. 2002-75556 (corresponding to WO 03/019280), Ser. No. 10/092,936, filed Mar. 6, 2002, corresponding to US Publication No. 2003-0053190, Ser. No. 10/179,997, filed Jun. 24, 2002, corresponding to US Publication No. 2003-0007238, Ser. No. 09/784,972, filed Feb. 15, 2001, corresponding to US Publication No. 2002-0182544 (corresponding to WO02/65215), Ser. No. 09/606,654, filed Jun. 28, 2000 (corresponding to WO02/01281), Ser. No. 09/874,391, filed Jun. 4, 2001, corresponding to US Publication No. 2002-0188053 (corresponding to WO 02/098977), Ser. No. 09/840,756, filed Apr. 23, 2001, corresponding to US Publication No. 2002-0176963 (corresponding to WO 02/086613), Ser. No. 10/229,530, filed Aug. 27, 2002, corresponding to US Publication No. 2003-0043450 (corresponding to WO 03/021346), Ser. No. 10/422,608, filed Apr. 23, 2003, Ser. No. 10/618,257, filed Jul. 10, 2003 and U.S. Pat. No. 6,545,797 the contents of all of which are incorporated herein by reference in their entirety.